I have an ex-racing TB who is THE most laid back, sensible horse I've ever met. Which is probably why he didn't do well on the track. Too quiet!
All kidding aside, I'd love to have a mule or mammoth donkey at some point, but a well trained one costs more than I can comfortably afford to spend, and you can't send a donk/mule to a horse trainer because they don't think like horses.
I do own a very quiet horse, that big draft mare....not that she thinks anything through, though....I have to think for her. I think everyone needs on of those quite, laid back, can't-tell -if-they-have-a-pulse horses :) Those are the only horses I want to own!
Yeah, even getting a well-trained mule or donkey requires training on your part because,a s you said, sending them away doesn't work, and every longear needs HIS owner to be his trainer. They get very one-mannish. If you own a longear, prepare to become his/her trainer :) They'll only respect you if you work with them first. I like that about them, though...because when it clicks, you really are a team.